Rheological properties of the extracellular polysaccharide from Agrobacterium sp.S-1231

A strain of Agrobacterium sp. S-1231 was isolated from one of the soil samples taken from Beijing area. In 4 days' cultivation it was found to produce extracellular polysaccharide and about 24 grams per liter of sugar-containing substrate. At the same concentrations, the polymer produced higher viscosity than that of xanthan gum (Kelzan). The viscosities of 0.2%, 0.5% and 1.0% solutions of this polymer were found to be 840, 5200 and 15000 cp respectively, measured with a Brookfield LVF viscosimeter at 6 rpm. Besides its pseudoplastic rheological properties and the excellent stability towards pH, it had unusual compatibility with high levels of salts and provided shear thinning properties similar to that in fresh water. Moreover, it is also compatible with cationic dyes without precipitation. Unlike other microbial polysaccharides, the viscosities of this polymer remained constant at different temperatures under 65 degrees C, but it decreased sharply in a narrow range of temperatures between 70-75 degrees C.